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ENVIRONMENT AND ENERGY
31 and clinics ( and some of the larger establishments ), particularly in the developing world , discharge medical waste untreated . Intensive farming methods and the profligate use of antibiotics in animal husbandry has resulted in high concentrations in municipal wastewater when such installations discharge to municipal sewers .
This entails the additional risk of antimicrobial drug resistance ( AMR ) ( Harris et al ., 2013 ). Other point sources can include intensive agricultural units and large stormwater outlets that serve hazardous or industrial areas . Table 5 gives estimated figures of wastewater production for commercial establishments and industries . Although not shown in this table , it is important to note that wastewater from food and beverage processing establishments also generally contain relatively high BOD concentrations . This type of waste is not difficult to treat and represents a great opportunity for energy recovery .
URBAN FORM AND THE POTENTIAL FOR MUNICIPAL AND URBAN WASTEWATER USE The potential for using municipal and urban wastewater is governed by several issues : first , the level of cross-contamination of wastewater and second , the application and its location . Water scarcity and the cost and availability of new water sources are also important factors .
Obviously , it is better to restrict the discharge of hazardous substances to sewers , particularly those that render the wastewater difficult to treat . Urban runoff , for example , could be directly reused for certain purposes , but once combined with blackwater , it would require additional treatment . The drivers for reuse are legislative and principally driven by economics .
If used water is available at a lower or a similar price ( including the cost of conveyance ), it will be considered over and above conventional freshwater sources . In some water-scarce countries or regions , necessity dictates and favours high levels of reuse .
Non-potable reuse : industrial The reuse of water in agriculture is one of the areas of great potential . It is already practised formally and informally in many countries . Reuse in peri-urban areas offers an opportunity to produce food close to the area of consumption .
Potable water reuse The use of treated municipal wastewater for drinking is not quite so common , though well-established in some places . The populations of some countries ,
BOX 2 : INDIRECT POTABLE REUSE IN PRACTICE , SAN DIEGO , CALIFORNIA San Diego is drinking recycled water because it imports 85 % of its water from Northern California and the Colorado River , into which upstream communities like Las Vegas discharge wastewater that is later treated for drinking purposes .
San Diego , which recycles sewage water for irrigation , invested USD11.8-million into an IPR study because of recent restrictions on Northern California water and drought in the Colorado River . The demo project at the North City Water Reclamation Plant ended in 2013 .
At that time , its Advanced Water Purification Facility was producing one million gallons of purified water each day , though no water is being sent to the reservoir . IPR is more economical for San Diego than recycling more sewage for irrigation because irrigation water would have to be conveyed through special purple pipes to separate it from potable water and expanding the purple pipe infrastructure would cost more than IPR .
Recycled water is also less expensive than desalinating seawater . In Orange County , for example , IPR costs USD800 – 850 to produce enough drinking water for two families of four for a year . Desalinating an equal amount of seawater would require USD1 200 – 1 800 because of the amount of energy needed . To deal with its growing population and salt intrusion into the groundwater , the Orange County Water District in California opened its USD480-million state-ofthe-art water reclamation facility , the largest in the US , in January 2008 .
It costs USD29-million a year to operate . After advanced water treatment , half the recycled water is injected into the aquifer to create a barrier against saltwater intrusion . The other half goes to a percolation pond for further filtration by the soils , and then after about six months , ends up in drinking water well intakes . By 2011 , it was estimated to be producing over 300 million litres a day .
Source : Extracted from Cho ( 2011 )
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www . plumbingafrica . co . za October 2018 Volume 24 I Number 8